Comparative study of in vitro caries-like lesions and natural caries lesions at crown margins

Secondary caries at crown margins and the influence of preparation techniques are major clinical problems. It was therefore the aim of this study to compare natural caries lesions at crown margins with experimental caries lesions.

Five extracted caries-free human molars were restored with gold cast crowns and afterwards covered with wax leaving a 3 x 3 mm window at the crown margin. These teeth were then incubated in acidified gel (pH 4.7) for 50 days. After incubation these teeth and five other crowned extracted teeth exhibiting natural caries lesions were embedded in Technovit 9100. Serial sections with a thickness of 80 microm were cut through the lesions and investigated with polarized light microscopy (PLM) and scanning electron microscopy (SEM) combined with energy dispersive X-ray (EDX) analysis for quantitative element analysis of Ca, P, and C. The results of the quantitative element analysis were statistically evaluated using the nonparametric ANOVA test for repeated measurements.

PLM of the experimental lesions showed homogeneous lesions with no transparent zone, or dead tracts. The natural caries lesions exhibited a demineralized zone, translucent zone, and dead tracts. Quantitative element analysis showed a statistically significant difference (p < 0.01) of Ca, P, and C between sound dentin and demineralized dentin in natural and experimental caries lesions.

The experimental model reproduces the demineralization pattern of secondary caries but does not simulate the vital dentin reactions of peritubular and intratubular mineralization.